The present invention relates to machines for treating running strips, tapes, webs or sheets of paper, textile, foil and/or analogous material, especially to improvements in systems of rolls which are utilized in calenders, printing plants, rolling mills or like machines or production lines wherein webs, strips, bands or sheets of flexible material are caused to advance along the peripheries and/or through the nips of two or more cooperating rolls. More particularly, the invention relates to improvements in systems of cooperating rolls wherein at least one roll has a shell whose material, at least in the region of the external surface of the shell, is a deformable (e.g., viscoelastic or rubber elastic) substance.
As a rule, the at least partly deformable (elastic) shell of the just discussed roll in a system of cooperating rolls in a calender or a like machine is mounted on and can rotate about a fixed carrier. The shell is propped by an adjusting unit which is installed in its interior and has at least one battery of force applying devices capable of compensating for flexure of corresponding portions of the shell to thus ensure that the width of the nip or nips which is or are defined by the shell with one or more neighboring rolls is at least substantially constant. To this end, the force applying devices are designed to apply to the internal surface of the shell forces of variable magnitude.
German Offenlegungsschrift No. 27 37 346 discloses a system of rolls wherein two rolls having elastically deformable shells are biased against the rigid shell of a third roll which is installed therebetween. The rolls with deformable shells are mirror symmetrical to one another with reference to a plane which includes the axis of the third roll. Each roll with a deformable shell has a plenum chamber which extends along the full length of the third roll and wherein the pressure of a fluid is variable in order to compensate for flexure of the respective deformable shell in a plane including its axis and the axis of the third roll. The plenum chamber is bounded by the shell of the respective roll, by the carrier for such shell, and by two longitudinally extending side walls or cheeks in the interior of the shell. In order to compensate for gravity-induced deformation of their shells, each of the rolls having a deformable shell comprises an elongated shoe which is installed in the respective shell between the carrier and the upper part of the shell and can be biased against the adjacent portion of the internal surface of the shell by a pressurized hydraulic fluid medium. Each shell comprises a rigid hollow cylindrical core and an elastically deformable liner which surrounds the core and whose external surface is adjacent to the external surface of the third roll. The liners consist of a viscoelastic fibrous material, such as paper. It is also known to make the liners from other elastic materials, e.g., from a textile carrier which is impregnated with a synthetic plastic substance, from a cast or extruded synthetic plastic material, or to utilize liners which consist (either entirely or in part) of natural or synthetic rubber.
It has been found that the temperature along the external surface of an elastically deformable shell, as considered in the axial direction of the roll, fluctuates within a rather wide range, for example, between 8 and 80.degree. C. The temperature peaks which develop within such range are likely to adversely affect, and to lead to actual destruction of, the elastic liner. Moreover, the temperature profile which is established in the longitudinal direction of the shell is likely to adversely influence the running webs of paper or other flexible material. Such undesirable influence of a rather wide range of temperatures upon the running web can develop irrespective of whether the deformable roll or rolls are equipped with the aforediscussed or other types of flexure compensating and/or preventing means.